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Ammonia

Test Overview

An ammonia test measures the amount of ammonia in the blood. Most
ammonia in the body forms when
protein is broken down by bacteria in the
intestines. The
liver normally converts ammonia into
urea, which is then eliminated in urine.

Ammonia levels in the blood rise when the liver is not able to
convert ammonia to urea. This may be caused by
cirrhosis or severe
hepatitis.

For this test, a blood sample may be taken from either a vein or an artery.

Why It Is Done

An ammonia test is done to:

Check how well the liver is working, especially
when symptoms of confusion, excessive sleepiness, coma, or hand tremor are
present.

Check the success of treatment for severe liver disease,
such as cirrhosis.

Help identify a childhood disorder called
Reye syndrome that can damage the liver and the
brain. Ammonia testing can also help predict the outcome (prognosis) of a
diagnosed case of Reye syndrome.

Help predict the outcome
(prognosis) of a diagnosed case of acute liver failure.

How To Prepare

Do not eat, drink anything other than water, or smoke for 8 hours
before having an ammonia blood test.

Avoid strenuous exercise just prior to having this test.

Tell your doctor if you:

Are taking any medicines. Many medicines can
interfere with test results. Your doctor may instruct you to stop taking
certain medicines for several days before having an ammonia
test.

Smoke or drink alcohol.

Talk to your doctor about any concerns you have regarding the need
for the test, its risks, how it will be done, or what the results may mean. To
help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).

How It Is Done

If the sample is taken from a vein

The health professional taking a sample of your blood will:

Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.

Clean the needle site with
alcohol.

Put the needle into the vein. More than one needle stick
may be needed.

Attach a tube to the needle to fill it with
blood.

Remove the band from your arm when enough blood is
collected.

Put a gauze pad or cotton ball over the needle site as
the needle is removed.

Put pressure on the site and then put on a
bandage.

If the sample is taken from an artery

A sample of blood from an artery is usually taken from the inside of the wrist (radial artery), but it can also be taken from an artery in the groin (femoral artery) or on the inside of the arm above the elbow crease (brachial artery). You will be seated with your arm extended and your wrist resting on a small pillow. The health professional drawing the blood may rotate your hand back and forth and feel for a pulse in your wrist.

To prevent the chance of damaging the artery of the wrist when the blood sample is taken, a procedure called the Allen test may be done to make sure that blood flow to your hand is normal. An ammonia test will not be done on an arm used for dialysis or if there is an infection or inflammation in the area of the puncture site.

The health professional taking a sample of your blood will:

Clean the needle site with alcohol. You may be given an injection of local anesthetic to numb that area.

Put the needle into the artery. More than one needle stick may be needed.

Allow the blood to fill the syringe. Be sure to breathe normally while your blood is being collected.

Put a gauze pad or cotton ball over the needle site as the needle is removed.

Put a bandage over the puncture site and apply firm pressure for 5 to 10 minutes (possibly longer if you take blood-thinning medicine or have bleeding problems).

How It Feels

If the sample is taken from a vein

The blood sample is taken from a vein in your arm. An elastic band
is wrapped around your upper arm. It may feel tight. You may feel nothing at
all from the needle, or you may feel a quick sting or pinch.

If the sample is taken from an artery

Collecting blood from an artery is more painful than collecting it from a vein because the arteries are deeper and are protected by nerves.

Most people feel a brief, sharp pain as the needle to collect the blood sample enters the artery. If you are given a local anesthetic, you may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin.

You may feel more pain if the person drawing your blood has a hard time finding your artery, your artery is narrowed, or if you are very sensitive to pain.

Risks

If the sample is taken from a vein

There is very little chance of a problem from having a blood sample
taken from a vein.

You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.

In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.

If the sample is taken from an artery

There is little chance of a problem from having a blood sample taken from an artery.

You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for at least 10 minutes after the needle is removed (longer if you have bleeding problems or take blood thinners).

You may feel lightheaded, faint, dizzy, or nauseated while the blood is being drawn from your artery.

On rare occasions, the needle may damage a nerve or the artery, causing the artery to become blocked.

Though problems are rare, be careful with the arm or leg that had the blood draw. Do not lift or carry objects for about 24 hours after you have had blood drawn from an artery.

Results

An ammonia test measures the amount of ammonia in the blood.
Results are usually available within 12 hours.

Normal

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

What Affects the Test

Reasons you may not be able to have the test or why the results may
not be helpful include:

Smoking.

Eating a high-protein or a low-protein
diet.

Using medicines that increase blood ammonia levels, such as
acetazolamide, valproate, and some
diuretics (such as furosemide).

Using medicines that decrease ammonia levels, such
as diphenhydramine, isocarboxazid, lactulose, neomycin, phenelzine, tetracycline, and tranylcypromine.

Strenuous exercise just before the test.

What To Think About

Ammonia levels do not always reflect the
severity of a person's symptoms. For example, a person with severe cirrhosis
may have only slightly elevated blood ammonia levels and yet may not be
thinking clearly or may be sleepy or in a coma. Other people with very high
ammonia levels may think and act normally.

Symptoms of a high
ammonia level, such as confusion or extreme sleepiness, may be treated with a
medicine called lactulose, a laxative that works by reducing ammonia production
in the
intestines.

It is common for newborns to
have slightly high levels of ammonia in their blood. But the levels are
temporary and usually do not cause symptoms.

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